1. Field of the Invention
The present invention relates to a milking device with at least one teat cup, which comprises an internal cavity for accommodating the teat of the animal to be milked through an opening of the teat cup as well as a pulse cavity separated from the internal cavity by a teat rubber, the said pulse cavity being able to be connected to a negative pressure source.
2. Brief Description of the Related Art
During the milking of animals, teat cups are normally used, which comprise an internal cavity for the accommodation of the teat of the animal to be milked, which is surrounded at its circumference by a teat rubber. A membrane, which is formed from an elastic material, is designated as the teat rubber. It is not essential that this is rubber. The teat rubber separates the internal cavity from a pulse cavity which is surrounded at its circumference by a teat cup housing. The pulse cavity regularly communicates through tubes with a source of negative pressure. During milking a negative pressure is first produced in the pulse cavity in the so-called suction phase, the negative pressure then being reduced in the so-called relief phase. In this relief phase the teat rubber, which is pulled outwards radially in the suction phase, collapses. A pulse cycle consists of a suction and a relief phase. The milked milk is drawn off via a milk line communicating with the internal cavity. A negative pressure is regularly produced in the internal cavity below the teat through this milk line, said negative pressure sucking the milk from the teat cup.
The pressure profile and the absolute pressure during the pulse cycle in the pulse cavity are controlled. Normally in this respect, each milking device, which comprises a number of teat cups equal to the number of teats on the animal to be milked, comprises a pulsator. The delivery of milk when milking an animal is stimulated with the set pressure difference profile, i.e. the pressure difference between the internal cavity and the pulse cavity and the temporal sequence of this pressure difference. First, in a so-called set-up phase, a specific movement of the teat rubber can then be imposed, which increases the readiness of the animal to deliver milk. Thereafter, the setting of a temporarily changing, cyclically recurring pressure profile occurs for drawing off the milk. The setting occurs in each case with regard to the desired movement of the teat rubber. In the relief phase this presses in particular circumferentially against the teat, whereas the teat is stretched in the circumferential direction during the suction phase.
With increasing automation and the more intensive employment of external workers and during milking, in particular of cows using automatic milking methods without human supervision, the requirement for automatic control of the most important functions of the milking system increases. These important functions also include the pressure conditions in the teat cup, in particular the radial pressure from the teat rubber acting on the teat.
In the attempts to define a possible automatic control of the most important functions it is initially obvious that the control signals in the pulsator should be monitored to enable conclusions to be drawn about the pressure relationships in the teat cup. However, this type of control only reproduces the electrical control signals, but not the actual pressure conditions in the teat cup. Pressure sensors built into the teat cup also only allow information to be obtained indirectly about the movement of the teat rubber, which can lead to erroneous assessments of the actual movement of the teat rubber. In particular, ageing processes on the teat rubber can lead to the pressure set-point values, once they are set as correct, no longer being obtained. This type of behavior cannot however be found, or only inadequately found, based on the measured pressure values in the individual pressure cavities. Also there is the problem of impairment or damage to the sensitive pressure sensors under the harsh conditions in practice.
From DE-A-198 02 887 a measurement device is known, which can be introduced through the opening into the internal cavity of a teat cup. This measurement device comprises a “measuring teat” which replicates the geometry of the teat and which has on its circumferential surface film circuit boards applied to the “measuring teat” on a basic body for the spatial resolution of a pressure signal. These are covered with a layer of foamed material and coated with a protective layer. The known measurement device is relatively complicated in construction and must be used at regular intervals for checking the milking device. These time intervals must be defined and monitored by trained operating personnel.